Intervals in music get their names from the major scale

For example C B is called a major seventh interval as startung from C and playing the C major scale the 7th step is B.


For example C E is called a major third interval as E is third and belongs to the C major scale.


D C# is a major sevnth interval as starting from D and playing the D major scale C# is the 7th note of the scale.


D F# is a major third as (F is the 3td step) and F# belongs to the D major scale.


Eb G is a major third interval as starting from Eb and playing the Eb major scale the 3rd nite of the scale is G.


Eb D is a major 7th interval.



So shouldn't the chord C E G B usually called C major 7th be called C major 3rd major 7th?


Of we may also have on other scales:


C Eb G B       C minor 3rd major 7th


C E G Bb       C major 3rd minor 7th


C Eb G Bb    C minor 3rd minor 7th



Reference:


Harmony - Piston - revised by DeVoto - 5th edition - classification of intervals - page 7